1. Field of the Invention
The present invention relates to an image display method for representing texture of a subject such as glossiness of a surface of a still subject or finely woven texture, an image processing method for this image display, an image processing apparatus for implementing this image processing method, a scan capturing apparatus for obtaining a captured image for performing the image display, and an image signal generation method for representing the texture of the subject.
2. Description of the Related Art
In these days, although it is possible to capture an image of a subject with a scanner or a camera to obtain a high quality image, it is difficult to reproduce texture such as glossiness of a substantially planar subject or fine unevenness on the surface of the subject by a raptured image obtained by photographing the subject. A method of representing texture of a subject includes processing by computer graphics (CG). For example, in three-dimensional data on a computer representing a subject, a specular reflection ratio, a diffuse reflection ratio, and the like are defined as information representing the texture, the three-dimensional data is subjected to rendering processing to calculate two-dimensional data and display the two-dimensional data as a two-dimensional image.
In general, the texture that a person feels, such as glossiness of a subject is obtained through a change in a state of specular reflection of the subject due to a change in a viewpoint of a viewer as in the case in which, when a person evaluates an object, he/she evaluates it while holding and shaking it by hands.
Therefore, in the above-mentioned CG, it is also necessary to subtly change a direction for illuminating a subject and perform rendering processing repeatedly such that specular reflection light changes dynamically. Since an amount of this rendering processing is large, time required for the rendering processing becomes extremely long.
Even if a processing speed of a computer further increases in future, it is still difficult to promptly generate realistic shape data and information on the texture of a subject using the method of the above-mentioned CG.
On the other hand, it has been proposed to perform modeling of three-dimensional data including information on the texture of a subject with a computer using a photographed image of the subject.
In JP 07-066436 B and JP 2001-108421 A, a method of photographing a plurality of images from different viewpoints to obtain three-dimensional data is proposed. However, since this method does not separate specular reflection light and diffuse reflection light, sufficient information on the texture of a subject cannot be obtained.
On the other hand, as a method of separating specular reflection light and diffuse reflection light in order to perform three-dimensional modeling of a subject, a method based on a dichroism reflection model is proposed (“Extraction of Specular Reflection Using Multiple Color and Range Images”, Otsuki, et al., The Institute of Electronics, Information and Communication Engineers Transaction, D-II Vol. J-80-D-II No. 6 pp. 1352–1359, June 1997).
However, in this method, a statistical processing for estimating a color vector is necessary and surfaces of a subject of a certain size with the identical texture are required. Thus, if different materials and colors are combined finely in a subject, it is difficult to use the above-mentioned method for this subject.
On the other hand, in JP 08-039841 A, there is proposed a method in which subject images with different directions of illumination are photographed to obtain a signal of a state in which reflected light is large and a signal of a state in which reflected light is small, and a glossiness signal representing glossiness of the subject is obtained from these two signals and used to provide glossiness by image forming means. However, since the image forming means used in this method does not give a dynamic change to an image of the subject, the feel of glossiness cannot be reproduced on the image. In addition, since the glossiness signal is obtained by subtracting the signal of a state in which reflected light is small from the signal of a state in which reflected light is large, it is also impossible to represent the texture of a woven fiber or the like having directionality in glossiness according to subtle unevenness of a subject.
Moreover, since glossiness is provided by the above-mentioned image forming means through re-heating by heat transfer, a fine texture of a subject cannot be controlled due to spread of heat by the re-heating. Therefore, there is a problem in that the feel of a woven fiber and wrinkle cannot be represented sufficiently.